U.S. patent number 8,437,093 [Application Number 13/444,473] was granted by the patent office on 2013-05-07 for projection lens system and projector apparatus.
This patent grant is currently assigned to Nittoh Kogaku K.K.. The grantee listed for this patent is Takahiko Matsuo. Invention is credited to Takahiko Matsuo.
United States Patent |
8,437,093 |
Matsuo |
May 7, 2013 |
**Please see images for:
( Certificate of Correction ) ** |
Projection lens system and projector apparatus
Abstract
A projection lens system has first, second and third lens
groups. The first lens group with combined focal length f1 has, in
order from a screen side, a first negative meniscus lens, a second
negative meniscus lens with focal length f12, refractive index n12
and screen side surface radius of curvature R12a, and a negative
biconcave lens with focal length f13. A second lens group consists
of a positive biconvex lens with a radius of curvature R21b of a
surface on a light modulator side of the positive biconvex lens.
The system satisfies the following conditions:
1.0<|f12/f1|<4.0; 5.0<|f13/f1|<9.0; 1.75<n12<2.0;
and 0.1<|R21b/R12a|<0.8.
Inventors: |
Matsuo; Takahiko (Suwa,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Matsuo; Takahiko |
Suwa |
N/A |
JP |
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|
Assignee: |
Nittoh Kogaku K.K. (Suwa-shi,
Jagano, JP)
|
Family
ID: |
47006221 |
Appl.
No.: |
13/444,473 |
Filed: |
April 11, 2012 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20120262803 A1 |
Oct 18, 2012 |
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Foreign Application Priority Data
|
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|
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Apr 13, 2011 [JP] |
|
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2011-89088 |
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Current U.S.
Class: |
359/784;
359/716 |
Current CPC
Class: |
G02B
13/18 (20130101); G02B 15/143507 (20190801); G03B
33/08 (20130101); G03B 21/2066 (20130101) |
Current International
Class: |
G02B
9/12 (20060101); G02B 3/02 (20060101) |
Field of
Search: |
;359/716,784 |
Foreign Patent Documents
Primary Examiner: Dinh; Jack
Attorney, Agent or Firm: Thompson Hine LLP
Claims
What is claimed is:
1. A projection lens system that projects projection light from a
light modulator onto a screen, comprising, in order from a screen
side thereof, a first lens group with negative refractive power, a
second lens group with positive refractive power, and a third lens
group with positive refractive power, wherein the first lens group
includes, in order from the screen side, a first negative meniscus
lens that is made of resin and is convex on the screen side, a
second negative meniscus lens that is made of glass and is convex
on the screen side, and a negative biconcave lens made of resin,
both surfaces of the first negative meniscus lens and of the
negative biconcave lens being aspherical, the second lens group
consists of a positive biconvex lens made of glass, and a combined
focal length f1 of the first lens group, a focal length f12 of the
second negative meniscus lens of the first lens group, a focal
length f13 of the negative biconcave lens of the first lens group,
a refractive index n12 of the second negative meniscus lens of the
first lens group, a radius of curvature R12a of a surface on the
screen side of the second negative meniscus lens of the first lens
group, and a radius of curvature R21b of a surface on a light
modulator side of the positive biconvex lens of the second lens
group satisfy following conditions 1.0<|f12/f1|<4.0,
5.0<|f13/f1|<9.0, 1.74<n12<2.0, and
0.1<R21b/R12a|<0.8.
2. The projection lens system according to claim 1, wherein
following conditions are also satisfied 2.0<|f12/f1|<3.5,
6.0<|f13/f1|<8.0, 1.80<n12<2.0, and
0.2<|R21b/R12a|<0.5.
3. The projection lens system according to claim 1, wherein a
thickness t11c at a center of the first negative meniscus lens of
the first lens group and a thickness t11e at an end of an effective
diameter of a surface on the light modulator side of the first
negative meniscus lens of the first lens group satisfy following
condition 4.0.ltoreq.t11e/t11c.ltoreq.5.0.
4. The projection lens system according to claim 1, wherein the
third lens group includes a first cemented lens, a second cemented
lens and a first positive biconvex lens.
5. The projection lens system according to claim 4, wherein the
first cemented lens is disposed on the screen side of the first
positive biconvex lens with one air gap in between and the second
cemented lens is disposed on the light modulator side of the first
positive biconvex lens with at least one air gap in between, the
first cemented lens consists of, in order from the screen side, a
positive biconvex lens and a negative biconcave lens, and a radius
of curvature R32b of a surface on the light modulator side of the
negative biconcave lens of the first cemented lens of the third
lens group and the radius of curvature R33a of a surface on the
screen side of the first positive biconvex lens of the third lens
group satisfy the following condition
0.89<R32b/R33a<1.01.
6. The projection lens system according to claim 5, wherein the
second cemented lens consists of, in order from the screen side, a
negative meniscus lens that is convex on the screen side, a
positive biconvex lens, and a negative meniscus lens that is convex
on the light modulator side, and the third lens group further
includes a second positive biconvex lens that is disposed on the
light modulator side of the second cemented lens.
7. The projection lens system according to claim 4, wherein the
first cemented lens is disposed on the light modulator side of the
first positive lens and the second cemented lens is disposed on the
light modulator side of the first cemented lens, the first cemented
lens includes, in order from the screen side, a negative meniscus
lens that is convex on the screen side and a positive biconvex
lens, the second cemented lens includes, in order from the screen
side, a positive biconvex lens and a negative meniscus lens that is
convex on the light modulator side, and the third lens group
further includes a second biconvex positive lens that is disposed
on the light modulator side of the second cemented lens.
8. A projector comprising: a projection lens system according to
claim 1; and a light modulator that modulates illumination light
and supplies modulated illumination light to the projection lens
system.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from the prior Japanese Patent Application No. 2011-89088, filed
Apr. 13, 2011, the entire contents of which are incorporated herein
by reference.
BACKGROUND
The present invention relates to a projection lens system of a
projector apparatus.
Japanese Laid-Open Patent Publication No. 2006-215476 discloses a
compact, wide-angle projection lens system that is suited to a
light modulator, such as a DMD, equipped with a plurality of
elements that generate an image by changing the direction of
reflection of light. Publication No. 2006-215476 states that by
using a arrangement where a negative first lens group and a
positive second lens group are disposed in that order from the
screen side, where the incident side is non-telecentric, where a
pair of doublet cemented lenses with positive refractive power and
with the cemented surfaces facing in opposite directions are
disposed on the screen side of the second lens group, and where a
triplet cemented lens with positive refractive power is disposed on
the light valve side, it is possible to effectively correct
curvature of field and provide a wide-angle projection lens system
that is compact and has a half angle of view of 47 degrees or
wider.
In applications such as presentations and education, there is
demand for a projection lens system that is more compact and is
even wider.
SUMMARY
One aspect of the present invention is a projection lens system
that projects projection light from a light modulator onto a
screen. This projection lens system includes, in order from the
screen side thereof, a first lens group with negative refractive
power, a second lens group with positive refractive power, and a
third lens group with positive refractive power. The first lens
group includes, in order from the screen side, a first negative
meniscus lens that is made of resin and is convex on the screen
side, a second negative meniscus lens that is made of glass and is
convex on the screen side, and a negative biconcave lens made of
resin, both surfaces of the first negative meniscus lens and of the
negative biconcave lens being aspherical. The second lens group
consists of a positive biconvex lens made of glass. A combined
focal length f1 of the first lens group, a focal length f12 of the
second negative meniscus lens of the first lens group, a focal
length f13 of the negative biconcave lens of the first lens group,
a refractive index n12 of the second negative meniscus lens of the
first lens group, a radius of curvature R12a of a surface on the
screen side of the second negative meniscus lens of the first lens
group, and a radius of curvature R21b of a surface on the light
modulator side of the positive lens of the second lens group
satisfy Conditions (1) to (4) below. 1.0<|f12/f1|<4.0 (1)
5.0<|f13/f1|<9.0 (2) 1.75<n21<2.0 (3)
0.1<|R21b/R12a|<0.8 (4)
This projection lens system has a negative-positive-positive
three-group arrangement and by making the three lenses of the first
lens group that is closest to the screen, i.e., on the enlargement
conjugate side, and is where the lens aperture (stop) is
comparatively large respectively out of resin, glass, and resin
lenses in that order, a low-cost, wide-angle, and compact
projection lens system is provided.
That is, since the negative refractive power would be insufficient
if all three lenses were made of resin to reduce cost, the
diameters of the lenses, and in particular the diameter of the lens
closest to the screen, would increase, which would make it
difficult to provide a compact projection lens system. If the focal
length of every lens were made shorter to make the lens system
compact, using resin for every lens would mean an increase in
curvature, which is undesirable since it makes it difficult to
correct aberration and increases the temperature-based variation in
lens performance.
In this projection lens system, by making the second negative
meniscus lens of the first lens group a glass lens with high
refractive power, it is possible to make the effective diameters of
the two resin lenses in front and behind comparatively smaller. In
addition, it is possible, without increasing the curvature of the
two resin lenses in front and behind, to provide a projection lens
system that is compact and favorably corrects aberration.
In addition, in this projection lens system, by setting the power
of the second negative meniscus lens made of glass stronger as
indicated by Condition (1), the power of the negative lens made of
resin can be made weaker as shown by Condition (2), which
suppresses temperature-based variation in lens performance,
particularly variation in the back focus. Also, when the power of
the second negative meniscus lens has been increased, by using a
glass material with a high refractive index as shown by Condition
(3), it is possible to avoid a large increase in curvature, which
suppresses the production of aberration.
That is, in this projection lens system, if the upper limit of
Condition (1) is exceeded, the power of the second negative
meniscus lens out of the total power of the first lens group
becomes weak, which makes it difficult to set the power of the
negative lens which is made of resin as weak relative to the power
of the first lens group as in the range shown in Condition (2).
Accordingly, it becomes difficult to provide a projection lens
system that is wide angle and has little variation in back focus
due to temperature variation. Also, although it is preferable for
the refractive index n12 of the second negative meniscus lens to be
high, by keeping the refractive index n12 within the range of
Condition (3), it is possible to prevent excessively high
dispersion and to favorably correct chromatic aberration.
In this projection lens system, since the second negative meniscus
lens has high negative refractive power, there is a tendency for
aberration to occur in the direction of divergence. Further, in
this projection lens system, the radius of curvature R21b of the
surface on the light modulator side of the positive lens of the
second lens group which is the closest surface on the reduction
conjugate side to the surface on the screen side of the second
negative meniscus lens to be set smaller (i.e., for the curvature
to be higher) relative to the radius of curvature R12a of the
surface on the screen side of the second negative meniscus lens, or
in other words, within the range of Condition (4). The aberration
is produced in the opposite direction (that is, the direction of
convergence) by the surface on the light modulator side of the
positive lens of the second lens group and the aberration of the
second negative meniscus lens can be favorably corrected.
In this projection lens system, Conditions (1') to (4') should
preferably also be satisfied. 2.0<|f12/f1|<3.5 (1')
6.0<|f13/f1|<8.0 (2') 1.80<n12<2.0 (3')
0.2<|R21b/R12a|<0.5 (4')
In this projection lens system, a thickness t11c at the center of
the first negative meniscus lens of the first lens group and a
thickness t11e at an end of an effective diameter of a surface on
the light modulator side of the first negative meniscus lens of the
first lens group should preferably satisfy Condition (5) below.
4.0.ltoreq.t11e/t11c.ltoreq.5.0 (5)
By designing the projection lens system to satisfy the range of
Condition (5), it is possible to favorably correct various
aberrations including astigmatism. If the upper limit of Condition
(5) is exceeded, the thickness t11e at the end of the effective
diameter of the first negative meniscus lens becomes large relative
to the center thickness t11c and since the difference in the amount
of light absorbed inside the lens becomes large between the center
and the periphery, there is a significant drop in peripheral
brightness. On the other hand, if the lower limit of Condition (5)
is exceeded, the thickness t11e at the end of the effective
diameter of the first negative meniscus lens becomes small relative
to the center thickness t11c, which makes it difficult to correct
various aberrations including astigmatism.
The third lens group should preferably include a first cemented
lens, a second cemented lens and a first positive biconvex lens. By
disposing a plurality of cemented lenses in the third lens group,
chromatic aberration correction performance is improved on the
reduction conjugate side. For this reason, the chromatic aberration
correcting performance of the first lens group is favorably
complemented, and a lens made of high-dispersion glass with an even
higher refractive index can be used as the second negative meniscus
lens. Accordingly, it is possible to construct a first lens group
suited to a more compact and wide angle lens system.
The first cemented lens can be disposed on the screen side of the
first positive lens with one (1) air gap in between, then the
second cemented lens is disposed on the light modulator side of the
first positive lens with at least one air gap in between. The first
cemented lens includes, in order from the screen side, a positive
biconvex lens and a negative biconcave lens, and that a radius of
curvature R32b of a surface on the light modulator side of the
negative lens of the first cemented lens and the radius of
curvature R33a of a surface on the screen side of the first
positive biconvex lens of the third lens group satisfy Condition
(6) below. 0.89<R32b/R33a<1.01 (6)
By designing the projection lens system so that the radii of
curvature of the facing surfaces of the negative lens and the
positive lens that are adjacent with one air gap in between are
within the range of Condition (6), the two surfaces that have
substantially the same radii of curvature can be aligned with the
same orientation. This means it is possible to achieve
significantly more favorable correcting performance for various
aberrations including comatic aberration.
The second cemented lens may include, in order from the screen
side, a negative meniscus lens that is convex on the screen side, a
positive biconvex lens, and a negative meniscus lens that is convex
on the light modulator side, and the third lens group may include a
second positive biconvex lens that is disposed on the light
modulator side of the second cemented lens.
The first cemented lens may be disposed on the light modulator side
of the first positive lens and the second cemented lens may be
disposed on the light modulator side of the first cemented lens,
the first cemented lens may include, in order from the screen side,
a negative meniscus lens that is convex on the screen side and a
positive biconvex lens, the second cemented lens may include, in
order from the screen side, a positive biconvex lens and a negative
meniscus lens that is convex on the light modulator side, and the
third lens group may further include a second biconvex positive
lens that is disposed on the light modulator side of the second
cemented lens.
Another aspect of the present invention is a projector including:
the projection lens system described above; and the light modulator
that modulates illumination light and supplies the modulated
illumination light to the projection lens system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing the overall construction of a projector
that uses a projection lens system according to the present
invention;
FIG. 2 is a diagram showing the overall arrangement of a projection
lens system according to a first embodiment of the present
invention;
FIG. 3 is a table showing lens data of the projection lens system
according to the first embodiment;
FIGS. 4A and 4B show various numeric values of the projection lens
system according to the first embodiment, with FIG. 4A showing
basic data and FIG. 4B showing aspherical surface data;
FIGS. 5A and 5B are aberration graphs of the projection lens system
according to the first embodiment, with FIG. 5A showing
longitudinal aberration and FIG. 5B showing lateral aberration;
FIG. 6 is a diagram showing the overall arrangement of a projection
lens system according to a second embodiment of the present
invention;
FIG. 7 is a table showing lens data of the projection lens system
according to the second embodiment;
FIGS. 8A and 8B show various numeric values of the projection lens
system according to the second embodiment, with FIG. 8A showing
basic data and FIG. 8B showing aspherical surface data;
FIGS. 9A and 9B are aberration graphs of the projection lens system
according to the second embodiment, with FIG. 9A showing
longitudinal aberration and FIG. 9B showing lateral aberration;
FIG. 10 is a diagram showing the overall arrangement of a
projection lens system according to a third embodiment of the
present invention;
FIG. 11 is a table showing lens data of the projection lens system
according to the third embodiment;
FIGS. 12A and 12B show various numeric values of the projection
lens system according to the third embodiment, with FIG. 12A
showing basic data and FIG. 12B showing aspherical surface
data;
FIGS. 13A and 13B are aberration graphs of the projection lens
system according to the third embodiment, with FIG. 13A showing
longitudinal aberration and FIG. 13B showing lateral
aberration;
FIG. 14 is a diagram showing the overall arrangement of a
projection lens system according to a fourth embodiment of the
present invention;
FIG. 15 is a table showing lens data of the projection lens system
according to the fourth embodiment;
FIGS. 16A and 16B show various numeric values of the projection
lens system according to the fourth embodiment, with FIG. 16A
showing basic data and FIG. 16B showing aspherical surface data;
and
FIGS. 17A and 17B are aberration graphs of the projection lens
system according to the fourth embodiment, with FIG. 17A showing
longitudinal aberration and FIG. 17B showing lateral
aberration.
DETAILED DESCRIPTION
FIG. 1 schematically shows a projector that uses a typical
projection lens system according to an embodiment of the present
invention. The projector (projector apparatus) 1 includes a light
modulator (light valve) 2, a light emitting system 3 that emits
illumination light 91 to be modulated by the light valve 2, and a
projection lens system 10 that projects projection light 92 that
has been reflected in an effective direction by the light valve 2
to project the light onto a screen 9. This projector 1 is a
single-panel video projector that uses a DMD (digital mirror
device) as the light valve 2 and the light emitting system 3
includes a white light source 4 such as a halogen bulb and a
disc-shaped rotating color splitting filter (or "color wheel") 5.
Light of the three primary colors red, green, and blue become
incident on the DMD (light valve) 2 according to time division. By
controlling elements that correspond to individual pixels at the
timing when the light of the respective colors is incident, a color
image is displayed. The light emitting system 3 further includes an
illumination lens system 7 that collects the light from the white
light source 4 and outputs the non-telecentric illumination light
91 via a mirror 6 or the like to the DMD 2.
First Embodiment
FIG. 2 shows a projection lens system 10 according to a first
embodiment of the present invention. This projection lens system 10
includes lenses that consists of, in order from a side near or to
the screen (screen side), a first lens group G1 with negative
refractive power, a second lens group G2 with positive refractive
power, and a third lens group G3 with positive refractive
power.
The first lens group G1 that is closest to the screen 9 has an
overall negative refractive power and is composed, in order from
the screen side, of a first negative meniscus lens L11 that is made
of resin and is convex on the screen side, a second negative
meniscus lens L12 that is made of glass and is convex on the screen
side, and a negative biconcave lens L13 that is made of resin. Both
surfaces of the first negative meniscus lens L11, that is, the
surface S1 on the screen side and the surface S2 on a side near or
to the DMD 2 (DMD side) are aspherical. In addition, both surfaces
of the negative lens L13, that is, the surface S5 on the screen
side and the surface S6 on the DMD side are aspherical. The first
negative meniscus lens L11 of the first lens group G1 is the lens
with the largest effective diameter (aperture) out of the
projection lens system 10.
The second lens group G2 has an overall positive refractive power
and is composed of a positive biconvex lens L21 that is made of
glass.
The third lens group G3 that is closest to the DMD 2 has an overall
positive refractive power and is composed, in order from the screen
9 side, of a first cemented lens (balsam lens, doublet) L3B1
composed of two lenses cemented together, a positive biconvex lens
(first positive lens) L33, and a second cemented lens (balsam lens,
triplet) L3B2 composed of three lenses cemented together. The first
cemented lens L3B1 is composed, in order from the screen side, of a
positive biconvex lens L31 and a negative biconcave lens L32. The
second cemented lens L3B2 is composed, in order from the screen
side, of a positive biconvex lens L34, a negative biconcave lens
L35, and a positive biconvex lens L36. The third lens group G3
includes the positive lens L34 that is the lens with the smallest
effective diameter (aperture) out of the projection lens system 10.
A flare stop FS is disposed on the screen side of the third lens
group G3 and blocks scattered light (unnecessary light) that could
cause flare and ghosts. A cover glass CG composed of a single sheet
of glass is disposed on the DMD side of the third lens group G3.
Note that the cover glass CG is not limited to a single sheet and
multiple sheets may be disposed.
The projection lens system 10 is composed, in order from the screen
side, of ten (10) lenses numbered L11 to L13, L21, and L31 to L36
that are grouped into the three lens groups G1 to G3 that
respectively have negative, positive, and positive refractive
power. This projection lens system 10 is a single-focus type lens
system that is incapable of zooming. The third lens group G3 is
fixed and does not move, but the first lens group G1 and the second
lens group G2 move along the optical axis 100 to adjust the focus
(i.e., to perform focusing).
With this projection lens system 10, by making the three lenses L11
to L13 of the first lens group G1 that is closest to the screen 9,
i.e., on the enlargement conjugate side 10a, and is where the lens
aperture is comparatively large, respectively out of resin, glass,
and resin lenses in that order, it is possible to provide a
low-cost, wide-angle, and more compact projection lens system 10.
Every three lenses could be made of resin to reduce cost, but the
negative refractive power would be insufficient and the diameters
of the lenses, in particular the diameter of the lens closest to
the screen would be larger, which would make it difficult to
provide a compact projection lens system. The focal length of every
lens could be made shorter to make the lens system compact, but
using resin for every lens would mean an increase in curvature,
which is undesirable since it makes it difficult to correct
aberration and increases the temperature-based variation in lens
performance.
In this projection lens system 10, by making the second negative
meniscus lens L12 of the first lens group G1 a glass lens with high
refractive power, such configuration makes the effective diameters
of the two resin lenses L11 and L13 in front and behind
comparatively smaller. In addition, without increasing the
curvature of the two resin lenses L11 and L13 in front and behind,
the projection lens system 10 that is compact and favorably
corrects aberration can be provided.
The projection lens system 10 is designed so that the combined
focal length f1 of the first lens group G1, the focal length f12 of
the second negative meniscus lens L12, the focal length f13 of the
negative lens L13, the refractive index n12 of the second negative
meniscus lens L12, the radius of curvature R12a of the surface S3
on the screen side of the second negative meniscus lens L12, and
the radius of curvature R21b of the surface S8 on the DMD side of
the positive lens L21 satisfy the following Conditions (1) to (4).
1.0<|f12/f1|<4.0 (1) 5.0<|f13/f1|<9.0 (2)
1.75<n12<2.0 (3) 0.1<|R21b/R12a|<0.8 (4)
In the projection lens system 10, by setting the power of the
second negative meniscus lens L12 made of glass stronger as
indicated by Condition (1), the power of the negative lens L13 made
of resin can be made weaker as shown by Condition (2), which
suppresses temperature-based variation in lens performance,
particularly variation in the back focus. Also, when the power of
the second negative meniscus lens L12 has been increased, by using
a glass material with a high refractive index as shown by Condition
(3), it is possible to avoid a large increase in curvature, which
suppresses the production of aberration.
In the projection lens system 10, if the upper limit of Condition
(1) is exceeded, the power of the second negative meniscus lens L12
out of the total power of the first lens group G1 becomes weak,
which makes it difficult to set the power of the negative lens L13
which is made of resin as weak relative to the power of the first
lens group G1 as in the range shown in Condition (2). Accordingly,
it becomes difficult to provide a projection lens system that is
wide angle and has little variation in back focus due to
temperature variation. Although it is preferable for the refractive
index n12 of the second negative meniscus lens L12 to be high, by
keeping the refractive index n12 within the range of Condition (3),
it is possible to prevent excessively high dispersion and to
favorably correct chromatic aberration.
In addition, since the second negative meniscus lens L12 of the
projection lens system 10 has high negative refractive power, there
is a tendency for aberration to occur in the direction of
divergence. To compensate the aberration, the surface S8 on the DMD
side of the positive lens L21 of the second lens group G2 that is
the closest surface being convex on the opposite side (DMD side) to
the surface S3 being convex on the screen side, is designed with a
radius of curvature R21b that is smaller than the radius of
curvature R12a of the surface S3. The aberration in the opposite
direction (that is, the direction of convergence) produced using
the surface S8 of the positive lens L21 favorably correct the
aberration of the second negative meniscus lens L12.
If the upper limit in Condition (1) is exceeded, the power
(refractive power) of the second negative meniscus lens L12 becomes
weak relative to the power of the first lens group G1, resulting in
insufficient negative refractive power. This means that it is
difficult to achieve a wide angle for the projection lens system
10. If the upper limit of Condition (2) is exceeded, the power of
the negative lens L13 also becomes weak relative to the power of
the first lens group G1, resulting in difficulty in achieving a
wide angle. If the lower limit of Condition (2) is exceeded, the
power of the negative lens L13 becomes strong relative to the power
of the first lens group G1, resulting in difficulty in suppressing
variation in back focus due to temperature variation for the
negative lens L13 which is made of resin.
If the upper limit of Condition (3) is exceeded, the second
negative meniscus lens L12 becomes highly dispersive, which makes
it difficult to correct chromatic aberration. If the lower limit of
Condition (3) is exceeded, the power of the second negative
meniscus lens L12 becomes weak, which makes it difficult to achieve
a wide angle for the projection lens system 10. If the upper limit
of Condition (4) is exceeded, it becomes difficult to correct the
aberration caused by the second negative meniscus lens L12. If the
lower limit in Condition (4) is exceeded, the power of the surface
S8 of the positive lens L21 becomes high and it becomes difficult
to correct aberration. In any of such situations, there is a
tendency for an increase in various aberrations, including comatic
aberration.
As the upper limit of Condition (1), 3.7 is more preferable, 3.5 is
even more preferable, and 3.4 is significantly more preferable. As
the lower limit of Condition (1), 2.0 is more preferable.
As the upper limit of Condition (2), 8.0 is more preferable. As the
lower limit of Condition (2), 5.5 is more preferable, 6.0 is even
more preferable, and 6.4 is significantly more preferable.
As the upper limit of Condition (3), 1.9 is more preferable. As the
lower limit of Condition (3), 1.78 is more preferable, and 1.80 is
significantly more preferable.
As the upper limit of Condition (4), 0.6 is more preferable, 0.5 is
even more preferable, and 0.4 is significantly more preferable. As
the lower limit of Condition (4), 0.2 is more preferable.
The arrangement in which the positive lens L21 that is made of
glass and has high power, the negative lens L13 that is made of
resin and has low power, the negative meniscus lens L12 that is
made of glass and has high power, and the negative meniscus lens
L11 that is made of resin and has low power are disposed in that
order from the incident side 10b toward the output side 10a is
extremely effective in achieving a wide angle and in correcting
aberration for the projection lens system 10.
In addition, the projection lens system 10 is designed so that the
center thickness t11c at the optical axis 100 of the first negative
meniscus lens L11 and the thickness t11e at an end of the effective
diameter of the surface S2 on the DMD side of the first negative
meniscus lens L11 satisfy Condition (5) below.
4.0.ltoreq.t11e/t11c.ltoreq.5.0 (5)
By designing the projection lens system 10 to satisfy the range of
Condition (5), it is possible to favorably correct various
aberrations including astigmatism. If the upper limit of Condition
(5) is exceeded, the thickness t11e at the end of the effective
diameter of the first negative meniscus lens L11 becomes large
relative to the center thickness t11c, the difference in the amount
of light absorbed inside the lens becomes large between the center
and the periphery. That causes a significant drop in peripheral
brightness. If the lower limit of Condition (5) is exceeded, the
thickness t11e at the end of the effective diameter of the first
negative meniscus lens L11 becomes small relative to the center
thickness t11c, which makes it difficult to correct various
aberrations including astigmatism.
In the projection lens system 10, to increase the power of the
second negative meniscus lens L12 made of glass, the refractive
index n12 of the second negative meniscus lens L12 is set high
according to Condition (3), and the correction of chromatic
aberration by the second negative meniscus lens L12 with a high
refractive index (high dispersion) tends to be insufficient. For
this reason, by disposing the two cemented lenses L3B1 and L3B2 in
the third lens group G3, the insufficiency in the chromatic
aberration correction on the enlargement conjugate side 10a is
compensated on the reduction conjugate side 10b. Accordingly, it is
possible to provide a projection lens system 10 in which various
aberrations including chromatic aberration are favorably
corrected.
As shown in FIG. 2, the third lens group G3 is composed, in order
from the screen side, of the first cemented lens L3B1 composed of
two lenses cemented together, the first biconvex positive lens
(positive lens) L33, and a cemented lens L3B2 composed of three
lenses cemented together. The first cemented lens L3B1 is disposed
on the screen side of the positive lens L33 with no other lens and
only one air gap d11 in between, and the second cemented lens L3B2
is disposed on the DMD 2 side of the positive lens L33 with no
other lens and only one air gap d13 in between.
The projection lens system 10 is designed so that the radius of
curvature R32b of the surface S11 on the DMD side of the negative
lens L32 of the first cemented lens L3B1 and the radius of
curvature R33a of the surface S12 on the screen side of the
positive lens (the first positive biconvex lens) L33 of the third
lens group G3 satisfy Condition (6) below.
0.89<R32b/R33a<1.01 (6)
By designing the projection lens system 10 so that the radii of
curvature of the facing surfaces S11 and S12 of the negative lens
L32 of the first cemented lens L3B1 and the positive lens L33 are
within the range of Condition (6), the two surfaces S11 and S12
that have substantially the same radii of curvature are aligned
with the same orientation and are disposed with the smallest or
nearly the smallest air gap d11 (in the present embodiment, 0.80
mm) in between without the two surfaces S11 and S12 being cemented
together. This means it is possible to achieve a chromatic
aberration correcting performance that is close to a triplet and it
is additionally possible to achieve a correcting performance for
various aberrations including comatic aberration.
FIG. 3 shows data of the respective lenses of the projection lens
system 10. FIGS. 4A and 4B show various numerical values for the
projection lens system 10. In the lens data, "Ri" represents the
radius of curvature (mm) of each lens (i.e., each lens surface)
disposed in order from the screen side, "di" represents the
distance (mm) between the respective lens surfaces disposed in
order from the screen side, "Di" represents the effective diameter
(mm) of each lens surface disposed in order from the screen side,
"nd" represents the refractive index (d line) of each lens disposed
in order from the screen side, and "vd" represents the Abbe number
(d line) of each lens disposed in order from the screen side.
In FIG. 3, "Flat" indicates a flat surface. In FIG. 4B, "En"
represents "10 to the power n". As one example, "E-06" represents
"10 to the power -6", and "E-11" represents "10 to the power -11".
Above explanations relating to the lens data are the same in the
following embodiments.
Both surfaces S1 and S2 of the first negative meniscus lens L11
disposed closest to the screen 9 in the first lens group G1 and
both surfaces S5 and S6 of the negative lens L13 disposed closest
to the DMD 2 in the first lens group G1 are aspherical. The
aspherical surfaces are expressed by the following expression using
the coefficients K, A, B, C, D, E, and F shown in FIG. 4B with X as
the coordinate in the optical axis direction, Y as the coordinate
in a direction perpendicular to the optical axis, the direction in
which light propagates as positive, and R as the paraxial radius of
curvature. This is also the case for the embodiments described
later.
X=(1/R)Y.sup.2/[1+{1-(1+K)(1/R).sup.2Y.sup.2}.sup.1/2]+AY.sup.4+BY.sup.6+-
CY.sup.8+DY.sup.10+EY.sup.12
The various values in the equations given in Conditions (1) to (6)
described above for the projection lens system 10 according to the
present embodiment are as follows. |f12/f1|=3.4 Condition (1)
|f13/f1|=6.0 Condition (2) n12=1.8010 Condition (3)
|R21b/R12a|=0.31 Condition (4) t11e/t11c=4.0 (where t11e=16.0
mm,t11c=4.0 mm) Condition (5) R32b/R33a=1.009 Condition (6)
FIGS. 5A and 5B are graphs showing longitudinal aberration and
lateral aberration of the projection lens system 10. As shown in
FIGS. 5A and 5B, various aberrations are all favorably corrected
and it is possible to project large, high-quality images onto the
screen 9. Note that spherical aberration is shown for the
respective wavelengths of 630 nm (dotted line), 550 nm (solid
line), 460 nm (dashed line). In addition, astigmatism and comatic
aberration are respectively shown for tangential rays (T) and
sagittal rays (S). This is also the case for the embodiments
described later.
The projection lens system 10 according to the first embodiment has
a simple and compact construction with 10 lenses and a maximum
diameter of around 70 mm, but is wide-angle with an angle of view
of 114.2 degrees (a half angle of view of 57.1 degrees) and a focal
length of 7.11, and is capable, with an f number of 2.79, of
projecting bright and sharp images, making it one example of a
projection lens system 10 with a favorable balance between cost and
performance.
Second Embodiment
FIG. 6 shows a projection lens system 20 according to a second
embodiment of the present invention. The projection lens system 20
is also composed, in order from the screen side, of ten lenses
numbered L11 to L13, L21, and L31 to L36 that are grouped into the
three lens groups G1 to G3 that respectively have negative,
positive, and positive refractive power. Since the composition of
the lens groups G1 to G3 and the forms of the respective lenses
included in the lens groups G1 to G3 are the same as in the first
embodiment, detailed description of the individual lenses is
omitted. This is also the case for the embodiments described
later.
FIG. 7 shows data on the respective lenses of the projection lens
system 20. FIGS. 8A and 8B show various numerical values for the
projection lens system 20. The various values in the equations
given in Conditions (1) to (6) described above for the projection
lens system 20 according to the present embodiment are as follows.
|f12/f1|=3.3 Condition (1) |f13/f1|=6.5 Condition (2) n12=1.8010
Condition (3) |R21b/R12a|=0.29 Condition (4) t11e/t11c=5.0 (where
t11e=15.0 mm,t11c=3.0 mm) Condition (5) R32b/R33a=1.008 Condition
(6)
FIGS. 9A and 9B are graphs showing longitudinal aberration and
lateral aberration of the projection lens system 20. As shown in
FIGS. 9A and 9B, various aberrations are all favorably corrected so
that it is possible to project large, high-quality images onto the
screen 9.
In this way, the projection lens system 20 increases the ratio
between the center thickness t11c and the effective diameter end
thickness t11e of the first negative meniscus lens compared to the
first embodiment to improve Condition (5). This means that it is
possible to provide a high performance projection lens system 20
capable, with an F number of 2.3, of obtaining even brighter and
sharp images.
Third Embodiment
FIG. 10 shows a projection lens system 30 according to a third
embodiment of the present invention. The projection lens system 30
is also composed, in order from the screen side, of ten lenses
numbered L11 to L13, L21, and L31 to L36 that are grouped into the
three lens groups G1 to G3 that respectively have negative,
positive, and positive refractive power.
The third lens group G3 is composed, in order from the screen side,
of a positive biconvex lens (first positive biconvex lens) L31, a
first cemented lens (balsam lens, doublet) L3B1 composed of two
lenses cemented together, a second cemented lens (balsam lens,
doublet) L3B2 composed of two lenses cemented together, and a
positive biconvex lens (second positive biconvex lens) L36. The
first cemented lens L3B1 is composed, in order from the screen
side, of a negative meniscus lens L32 that is convex on the screen
side and a positive biconvex lens L33. The second cemented lens
L3B2 is composed, in order from the screen side, of a positive
biconvex lens L34 and a negative meniscus lens L35 that is convex
on the DMD side.
In this way, in the projection lens system 30, two cemented lenses
L3B1 and L3B2 that are both composed of two lenses cemented
together and the second positive lens L36 are disposed in the third
lens group G3.
FIG. 11 shows data on the respective lenses of the projection lens
system 30. FIGS. 12A and 12B show various numerical values for the
projection lens system 30. The various values in the equations
given in Conditions (1) to (5) described above for the projection
lens system 30 according to the present embodiment are as follows.
|f12/f1|=3.6 Condition (1) |f13/f1|=6.1 Condition (2) n12=1.8010
Condition (3) |R21b/R12a|=0.37 Condition (4) t11e/t11c=4.0 (where
t11e=16.0 mm,t11c=4.0 mm) Condition (5)
FIGS. 13A and 13B are graphs showing longitudinal aberration and
lateral aberration of the projection lens system 30. As shown in
FIGS. 13A and 13B, various aberrations are all favorably corrected
so that it is possible to project large, high-quality images onto
the screen 9.
Accordingly, with the projection lens system 30, by changing the
combination of lenses that are cemented together in the first
cemented lens L3B1 and the second cemented lens L3B2 of the third
lens group G3, it is possible to omit the cemented lens composed of
three lens cemented together, making this one example of a low-cost
projection lens system 30.
Fourth Embodiment
FIG. 14 shows a projection lens system 40 according to a fourth
embodiment of the present invention. The projection lens system 40
is composed, in order from the screen 9 side, of eleven lenses
numbered L11 to L13, L21, and L31 to L37 that are grouped into the
three lens groups G1 to G3 that respectively have negative,
positive, and positive refractive power. For use of the projection
lens system 40, an integrator such as a fly's eye lens and a TIR
prism are used and the projection light 92 that is incident to the
projection lens system 40 is telecentric.
The third lens group G3 is composed, in order from the screen side,
of a first cemented lens L3B1 composed of two lenses cemented
together, a positive biconvex lens (first positive biconvex lens)
L33, a cemented lens L3B2 composed of three lenses cemented
together, and a positive biconvex lens (second biconvex positive
lens) L37. The first cemented lens L3B1 is composed, in order from
the screen side, of a positive biconvex lens L31 and a negative
biconcave lens L32. The second cemented lens L3B2 is composed, in
order from the screen side, of a negative meniscus lens L34 that is
convex on the screen side, a positive biconvex lens L35, and a
negative meniscus lens L36 that is convex on the DMD side.
In this way, in the projection lens system 40, the positive lens
(second positive lens) L37 is additionally disposed on the DMD side
of the second cemented lens L3B2 of the third lens group G3. A stop
S is disposed on the screen side of the third lens group G3. A
cover glass CG made of a single sheet of glass with a large
thickness d20, in the present embodiment 25.00 mm is disposed on
the DMD 2 side of the third lens group G3.
FIG. 15 shows data on the respective lenses of the projection lens
system 40. FIGS. 16A and 16B show various numerical values for the
projection lens system 40. The various values in the equations
given in Conditions (1) to (6) described above for the projection
lens system 40 according to the present embodiment are as follows.
|f12/f1|=3.5 Condition (1) |f13/f1|=6.5 Condition (2) n12=1.8010
Condition (3) |R21b/R12a|=0.30 Condition (4) t11e/t11c=5.0 (where
t11e=15.0 mm,t11c=3.0 mm) Condition (5) R32b/R33a=0.89 Condition
(6)
FIGS. 17A and 17B are graphs showing longitudinal aberration and
lateral aberration of the projection lens system 40. As shown in
FIGS. 17A and 17B, various aberrations are all favorably corrected
so that it is possible to project large, high-quality images onto
the screen 9.
The projection lens system 40 that has the second positive lens L37
on the DMD side of the second cemented lens L3B2 of the third lens
group G3 is favorable for making the incident projection light 92
telecentric or near-telecentric and obtaining sharp images even if
the projector 1 is slightly moved in the direction of the optical
axis 100.
Note that the present invention is not limited to the embodiments
described above and is defined by the scope of the appended patent
claims. The projection lens system 10 (20, 30, 40) according to the
present invention can also be installed in a three-panel projector
capable of splitting light from the white light source 4 into three
colors using dichroic filters (mirrors) or the like. The light
modulator 2 may be an LCD (Liquid Crystal Display) panel and may be
a single panel that reproduces images of the respective colors
using time division or may have images of the respective colors
combined using a dichroic prism or the like.
* * * * *